Although several members of the class of organic thiocarbonates have been known for many years and various routes have been employed for their synthesis, the s,s′-bis-(α,α′-disubstituted-α″-acetic acid)-trithiocarbonate compounds of the present invention have not been disclosed. Trithiocarbonate compounds have been claimed for various applications, such as pesticides for agriculture, and also as lubricating oil additives.
Traditional methods of producing block copolymers, such as by living polymerization or the linking of end functional polymers, suffer many disadvantages, such as the restricted type monomers which can be utilized, low conversion rates, strict requirements on reaction conditions, and monomer purity. Difficulties associated with end linking methods include conducting reactions between polymers, and problems of producing a desired pure end functional polymer. The s,s′-bis-(α,α′-disubstituted-α″-acetic acid)-trithiocarbonate compounds of the present invention can alleviate the above noted problems and difficulties when utilized in free radical polymerizations.
The prior art WO98/01478 reference discloses the use of thiocarbonates to conduct living free radical polymerizations. The reference is limited to alkyl and benzyl functional groups, and is unable to make any aryl or carboxylic acid substituted trithiocarbonates with general methods known to the art. Synthesis, p 894 (1986), J. Chemical Research (Synopsis), p 478 (1995), and Synthetic Communications, Vol. 18, p 1531 (1988). We have also found the conversion for the dibenzyl derivatives disclosed in their example 26 to be very slow compared to the present invention when polymerizing acrylate, as can be seen in the Example section of this application. The WO/01478 reference states in the background that experiments have shown that dithiocarbamate derivatives have low transfer constants and are substantially ineffective in conferring living characteristics to radical polymerizations.
Macromolecules, 32, p 6977-6980 (1999) states that
dithiocarbamate compounds:
cannot control polymerization and are not effective RAFT agents. Additionally, carboxyl end groups cannot be formed utilizing the processes disclosed. Also WO 99/35177 and Macromolecules, Rapid Communications, 21, p 1035-1039 (2001) finds that R, R1, and R2 need to be fine tuned to control polymerization, meaning there is no guarantee all dialkyl dithiocarbamate will work as RAFT agents. Moreover, the substituent of the single bonded sulfur atom cannot be a carboxylic acid containing group in their synthesis.
U.S. Pat. No. 6,153,705 relates to a process for polymerizing block polymers of general formula (I):
in which process the following are brought into contact with each other:
an ethylenically unsaturated monomer of formula:CYY′(═CW—CW′)aH2,                a precursor compound of general formula (II):        
                and a radical polymerization initiator.        
Macromolecule Rapid Communications 2001, 22, p 1497-1503 and U.S. Pat. No. 6,153,705 disclose various xanthate compounds. The references cannot prepare the xanthate compounds of the present invention utilizing the methods disclosed within the references. 1) Alkylation with tertiary alkyl halides disclosed in the '705 patent will result in elimination, not substitution. The α-halo-α′,α″-dialkylacetic acid disclosed by the reference cannot be alkylated. 2) The compounds of the present invention contain a tertiary carbon attached to the single bonded sulfur atom of the compound. The '705 patent preferably utilizes an R1 group having a secondary carbon atom which results in a lower chain transfer coefficient than the present invention. Moreover, the xanthates disclosed by the references have been found to be less effective.
Unexpectedly, in view of the prior art, the compounds of the present invention are able to confer living characteristics to a free radical polymerization.